Numerical and experimental investigation on process parameters optimization in plastic injection molding for weldlines reduction and clamping force minimization

Weldlines are one of the major defects in plastic injection molding (PIM). The weldlines have an influence on not only the appearance of product but also the strength, so it is important to reduce the weldlines as much as possible. The melt plastic will be quickly solidified with the low weldline temperature that makes the weldlines long. On the other hand, clamping force also affects the product quality, but the relationship between the weldlines and the clamping force is rarely discussed in the literature. In this paper, the minimum weldline temperature is maximized for the weldlines reduction, whereas the clamping force is minimized for the high product quality. Therefore, a multi-objective design optimization of the process parameters is performed and the pareto-frontier between them is identified. Numerical simulation in PIM is generally so intensive that a sequential approximate optimization using a radial basis function network is used to identify the pareto-frontier. 3D cooling channel is used for the design optimization. Through the numerical simulation, the trade-off between the minimum weldline temperature and the clamping force is clarified. In addition, it is found that the 3D cooling channel is effective for the weldlines reduction and clamping force minimization, compared with the straight-type cooling channel. Finally, to examine the validity of the proposed approach, the experiment using the PIM machine (GL30-LP, Sodick) is carried out. It is found through the experimental result that the weldlines are reduced by the proposed approach.